Full movie description "Doctor Who The Androids of Tara: Part Three":

The Doctor kills the android princess, Count Grendel finds his plans foiled and can not find an opening to kill the new king (especially since the King's head bodyguard now suspects him of treachery against the King). So he offers Romana up in exchange to the Doctor for his own safety. But the Count has built another android programmed to kill the Doctor once it hears the Doctor's voice. Meanwhile, the real Romana escapes Grendel's castle and tries to ride for help.